This invention relates generally to store carriers for mounting a releasable store on an aircraft and, more particularly, to a stores ejection system from which a store is released with ejective force applied at forward and aft locations by thrusters which are actuated by cold, clean pressurized gas, such as air.
The store referred to herein may be used to contain munitions (i.e. "bombs"), or to contain other material to be dropped from an aircraft. Military aircraft used to dispense bombs, rockets, and other stores in flight usually include racks located beneath the wings and fuselage designed to release the stores upon command. Typical racks are shown in U.S. Pat. Nos. 4,043,525 and 4,347,777, both by the same inventor and assignee as in the present application and incorporated herein by reference.
At the time of target acquisition, a release mechanism is activated which results in mechanical release and subsequent forcible ejection of that weapon away from the aircraft. State of the art bomb ejector racks utilize pyrotechnic (explosive) cartridges which, on ignition, generate high pressure gas for actuating the mechanical release mechanism, as well as for providing high pressure to ejection rams which forcibly eject the store from the aircraft. This method was originated at Douglas Aircraft Company (now an operating division of McDonnell Douglas Corporation) in 1944, and is the current method used on virtually all weapon release devices.
While such pyrotechnic cartridges provide a weight efficient means of storing and releasing energy as a power source, they also have certain undesirable characteristics. For example, a great deal of cleaning and maintenance is required after firing a pyrotechnic device. When fired, the chemical burning of the explosive charge within the pyrotechnic cartridge results in a large amount of residue being deposited within the system. This residue also contains moisture and corrosives. After burning, the moisture in the system tends to further gather debris, form ice, and otherwise clog the internal and external workings of the bomb rack mechanism. Thus, if not properly disassembled and cleaned after a scheduled number of firings, at the cost of a great deal of labor and downtime for the aircraft, the stores rack will quickly become corroded and unreliable, and the required replacement maintenance interval will become unacceptably short.
Other problems associated with the use of pyrotechnic cartridges in bomb ejector systems include the necessity for use of hazardous cleaning solvents, which pose their own unique stowage, use, handling, and disposal considerations. Additionally, ground crew post-flight action is required to remove and dispose of the spent cartridges. Removal of live cartridges is required prior to off-loading unreleased stores, further increasing crew workload and turnaround time. Furthermore, prior to cartridge installation, the ground crew must utilize special equipment to conduct stray voltage checks, in order to assure that an inadvertent firing will not occur. Logistically, adequate supplies of cartridges must be maintained to support bomb rack operation, which imposes additional unique shipping, storage, and handling requirements because of their explosive nature. Cartridges have a limited shelf life as well, before becoming unreliable, so date monitoring and inventory control is necessary. Finally, parts life of the stores rack is limited because of the effects of pyrotechnic gas erosion, resulting in significant logistic and cost burdens.
Stores ejection systems are known in the prior art which avoid the use of pyrotechnic cartridges. For example, U.S. Pat. No. 4,204,456 to Ward discloses a pneumatic bomb ejector, which uses a suitable pressurized gas, such as air or nitrogen, as a stored energy source for actuating the ejector. However, the system is disclosed as being utilizable only with a particular type of customized mechanism which does not employ ejector rams to forcibly eject the store. This means that it may only be used for applications wherein it is not necessary to ensure that the store clears the aircraft slipstream by forcibly ejecting it away from the aircraft. Furthermore, the Ward system is not adaptable to the standardized ejection systems in use in almost all existing military aircraft, limiting its practical applicability. Another problem with the Ward system is that the gas is pre-charged prior to operation. However, as the aircraft climbs to altitude, and the ambient temperature drops, the pressure level drops as well. As the pressure level varies, so does the performance output. Without an onboard pressure maintenance system, the stores ejector may not operate reliably.
Another device which avoids the use of pyrotechnic cartridges is disclosed in U.S. Pat. No. 4,095,762 to Holt. This device includes a system which uses accumulator stored gas (nitrogen is disclosed) as an energy source, but uses a hydraulic subsystem as the energy transfer medium; i.e. the medium used to actuate the ram ejectors. As in Ward, the patentee apparently believed that the accumulator pressure alone is inadequate to function to actuate the ram ejectors. Ward chose therefore to eliminate ram ejectors, while Holt chose to employ a hydraulic energy transfer medium. Disadvantages of Holt's approach include a relatively complicated and heavy dual fluid system, and no onboard pressure replenishment system. Thus, as in the Ward system, as the pressure level varies due to temperature changes, so too does performance output.
An additional problem with the Holt system is that, at the end of the stores ejection event, recocking is required to retract the pistons. When using the stored accumulator pressure, this is accomplished manually after landing. The implication is that some residual pressure remains in the accumulator, which may pose safety concerns. Additionally, the ejector pistons remain extended until after landing and discharging, which increases both drag and radar signature, and is therefore a generally undesirable characteristic.
Still another prior art approach is discussed in U.S. Pat. No. 4,905,568 to Hetzer et al. This patent discloses an ejector mechanism which, like that of Holt, utilizes high pressure gas (again preferably nitrogen) as an energy source, with hydraulics as the energy transfer medium. Hetzer does attempt to compensate for pressure variations in the stored accumulator gas by employing heating coils to alter temperature of the gas as altitude changes. However, no onboard pressure regeneration or recharging system is disclosed or suggested.
What is needed, therefore, is a stores ejection system which employs ejector ram pistons for forcibly ejecting the store away from the aircraft, yet is much more simple, easy to maintain, and durable than systems of that type which are currently available.